vmsig: a neutral signaling layer between sensors/input and controls

An epoll-driven, neutral transfer-event bus that connects sensors and input
actuators to one or more controls, bidirectionally. It owns the transfer context
and events — delivery order, priority, protocol-level timing, and an
interrupt-driven event model over fd sources (eventfd/timerfd/sockets) — and
stays agnostic to both the sensor/input drivers and the control.

What lives here:
- memctx: a coherent address-space context per endpoint — the guest address-space
  root paired with a pre-opened read-only RAM-region fd, with per-endpoint epoch
  invalidation and retained replay to late subscribers. Perception lives in
  out-of-tree sensor libraries that consume this datum read-only.
- exclusive-ownership leases for destructive resource classes (input, power,
  memory-write).
- write-signaled memory writes (MEMWRITE): an atomic write to guest memory routed
  through the seam under an exclusive lease, never a writable mapping.
- a host-management seam for VM lifecycle/status and a neutral input-injection
  command path.
- multi-VM endpoints; capability-gated, audited control authorization over an
  in-process or unix-socket transport.

Builds against headers only by default (a stub mode that exercises the seam
without a VM); armed builds link the real sensor/input libraries behind flags.

src/adapter/memctx/include/memctx.h

@@ -0,0 +1,20 @@
+#ifndef VMSIG_MEMCTX_CFG_H
+#define VMSIG_MEMCTX_CFG_H
+#include <stdint.h>
+
+/* Private config of the memctx adapter (vmie). Passed as opaque to open(); NOT
+ * public (layout per reference: src/<module>/include/). cfg==NULL => stub. */
+typedef struct {
+    int         stub;       /* 1 => synthetic kcr3/RO-fd (spine without a VM)           */
+    const char* ram_path;   /* armed: path to guest RAM backing (NOT published outward) */
+    uint64_t    low;        /* below-4G split (vmie_win32_open / locator.low)           */
+    int         ro_fd;      /* >=0 => infra supplied a pre-sealed RO-fd (policy);       */
+                            /* <0  => default: open(ram_path, O_RDONLY) / stub-memfd    */
+} vmsig_memctx_cfg;
+
+/* Max SRC bytes per atomic gva_write (bounds the worker POD slot; mc_req header + src
+ * must stay <= VMSIG_WORK_SLOT). Private to the adapter (an executor bound), NOT part of
+ * the neutral control contract — control only needs VMSIG_MEMWRITE_INLINE for inline SRC. */
+#define VMSIG_MEMWRITE_MAX 192u
+
+#endif /* VMSIG_MEMCTX_CFG_H */